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C++: Account for chi nodes in back-edge detection

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This commit is contained in:
Jonas Jensen
2019-01-25 15:32:19 +01:00
parent 560dbdf984
commit ba8bf94d7b
4 changed files with 26 additions and 10 deletions
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15
cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/SSAConstruction.qll
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@@ -280,9 +280,18 @@ cached private module Cached {
cached Instruction getInstructionBackEdgeSuccessor(Instruction instruction, EdgeKind kind) {
exists(OldInstruction oldInstruction |
oldInstruction = getOldInstruction(instruction) and
result = getNewInstruction(oldInstruction.getBackEdgeSuccessor(kind)) and
not Reachability::isInfeasibleInstructionSuccessor(oldInstruction, kind)
not Reachability::isInfeasibleInstructionSuccessor(oldInstruction, kind) and
// There is only one case for the translation into `result` because the
// SSA construction never inserts extra instructions _before_ an existing
// instruction.
getOldInstruction(result) = oldInstruction.getBackEdgeSuccessor(kind) and
// There are two cases for the translation into `instruction` because the
// SSA construction might have inserted a chi node _after_
// `oldInstruction`, in which case the back edge should come out of the
// chi node instead.
if hasChiNode(_, oldInstruction)
then instruction = getChiInstruction(oldInstruction)
else instruction = getNewInstruction(oldInstruction)
)
}

15
cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/SSAConstruction.qll
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@@ -280,9 +280,18 @@ cached private module Cached {
cached Instruction getInstructionBackEdgeSuccessor(Instruction instruction, EdgeKind kind) {
exists(OldInstruction oldInstruction |
oldInstruction = getOldInstruction(instruction) and
result = getNewInstruction(oldInstruction.getBackEdgeSuccessor(kind)) and
not Reachability::isInfeasibleInstructionSuccessor(oldInstruction, kind)
not Reachability::isInfeasibleInstructionSuccessor(oldInstruction, kind) and
// There is only one case for the translation into `result` because the
// SSA construction never inserts extra instructions _before_ an existing
// instruction.
getOldInstruction(result) = oldInstruction.getBackEdgeSuccessor(kind) and
// There are two cases for the translation into `instruction` because the
// SSA construction might have inserted a chi node _after_
// `oldInstruction`, in which case the back edge should come out of the
// chi node instead.
if hasChiNode(_, oldInstruction)
then instruction = getChiInstruction(oldInstruction)
else instruction = getNewInstruction(oldInstruction)
)
}

4
cpp/ql/test/library-tests/ir/ir/aliased_ssa_ir.expected
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@@ -4687,5 +4687,5 @@ ir.cpp:
# 1059| r3_8(int) = Constant[0] :
# 1059| r3_9(bool) = CompareGT : r3_4, r3_8
# 1059| v3_10(void) = ConditionalBranch : r3_9
#-----| False (back edge) -> Block 2
#-----| True (back edge) -> Block 1
#-----| False -> Block 2
#-----| True -> Block 1

2
cpp/ql/test/library-tests/ir/ir/aliased_ssa_sanity.expected
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@@ -8,6 +8,4 @@ operandAcrossFunctions
instructionWithoutUniqueBlock
containsLoopOfForwardEdges
lostReachability
| ir.cpp:1060:12:1060:12 | Constant: (char)... |
| ir.cpp:1061:1:1061:1 | NoOp: return ... |
backEdgeCountMismatch